In a wireless telecommunication system, the communication of control signals, voice, data, and the like, are effectuated via a radio communications link established between a base station and one or more mobile stations, such as a mobile telephone, cell phone, personal data assistant (PDA), and the like. The radio communication link includes at least one antenna at the base station and at least one antenna at the mobile station.
Due to a number of environmental factors and conditions, such as fading, multi-path transmissions, and the like, it has been found that the capacity of a system may be increased using transmit diversity in the space domain or in the time domain, i.e., wherein a base station uses two or more spaced-apart antennas, and/or wherein signals transmitted from one antenna are delayed with respect to another antenna, or a combination thereof.
In an open-loop system, in which a base station receives no feedback from a mobile station indicating which antenna of multiple antennas provides the strongest channel of communication, then transmit power is typically apportioned equally between each antenna. However, in a closed-loop system, in which a base station does receive feedback from a mobile station indicating which antenna of multiple antennas provides the strongest channel of communication, then communication efficiency may be improved by assigning greater transmit power to the antenna having the better channel. Transmit power is thus “weighted” differently between the two antennas in an closed-loop system, resulting in improved communication efficiency, but also in an imbalance of transmit power between the antennas. Thus, transmit power that is available for use on an antenna with a weaker channel goes unused and., hence, is wasted.
If there are multiple users competing for access to a limited number of resources, such as base station antennas, then cost functions are implemented to prioritize the sequence in which users are scheduled for transmission of data based on a number of factors, such as service subscribed to, time in queue, and the like. If the transmission of data for a first-priority user does not require the power available for an antenna, then a determination is made whether the remaining power is sufficient to transmit data for one or more additional users next in priority and, if there is, then data for the additional users is transmitted simultaneously with the data for the first-priority user.
A drawback with using the aforementioned cost function is that it may result in a substantial portion of power available on one or more antennas of multiple antennas remaining substantially unused, or underused and, thus, wasted.
In an attempt to use more of the power available on all antennas, data from next-in-priority users that have relatively strong channels on antennas, having power that is not fully utilized, is transmitted from such antennas. While such techniques more efficiently utilize available power on all antennas, there typically still remains substantial unused, and hence wasted, power.
Accordingly, a continuing search has been directed to the development of a system and method for more efficiently utilizing power (i.e., minimizing unused power) available on each antenna of a system having multiple antennas.